The utility of QuantiFERON-TB Gold assay in patients with leprosy: A possible measure of anergy

We recently reported a tuberculosis-negative patient with leprosy, who displayed a giant purified protein derivative (PPD) reaction and had a positive QuantiFERON-TB Gold (QTF; Cellestis, Valencia, CA) test result.¹ Concurrently, work was published showing Mycobacterium tuberculosis antigens, early secretory antigenic target (ESAT)-6 kd and culture filtrate protein (CFP)-10 kd, are cross-reactive with M leprae and can lead to false-positive QTF results.² This supports the notion that QTF assays cannot reliably measure, in patients with leprosy, latent infection with M tuberculosis.